11
DEFROST
Once ice forms in an evaporator coil it keeps building more ice and eventually will lead
to equipment failure if not manually defrosted.
Some symptoms of ice forming in the coil are:
1.
loss of air circulation and air throw
2.
loss of room temperature.
3.
no off-cycle time.
4.
flood back.
5.
water spitting out of the fans or coil on air defrost systems.
Long term ice formation will crush the refrigerant tubes in the coil causing leaks and
major equipment problems. If ice formation is suspected, carefully check the interior
rows of the coil with a good light. Ice formation usually starts at the bottom of the coil
in the middle rows and can be difficult to detect.
For most applications, two to four defrost cycles per day should be adequate. The
defrost requirements will vary on each installation so the defrost settings should be
determined by observing the system operation.
Air defrost
The normal “off cycle” of the compressor
may be adequate to keep the evaporator
coil clear of frost. In other applications, a
defrost timer may be necessary to help
assure a clear coil in a medium
temperature environment, “Air defrost” is
initiated by the timer, but the evaporator
fans continue to operate to facilitate the
melting of frost on the fan surface. Other
types of defrost schemes require that the
fans on the evaporator shut off during the
defrost period.
Electric defrost
The
recommended
electric
defrost
circuitry is typically using a defrost
heater.
During defrost cycle, compressor and fan
are stopped automatically by the timer at
predetermined times.
In generally, electric defrost uses defrost
timer for preventing over heating.
There are two kinds defrost timers.
Turbo air uses bimetal method.
During the defrost cycle, if the room
temperature rises above the desired
setting, defrost heater will turn off
automatically and if the room temperature
drops lower than desired temperature,
Defrost heater will turn off.
If the defrost time finished, defrost timer
will turn on and the compressor and fans
will run continuously.
At this time, fan power is supplied later
